The present invention relates to an electric-mechanical-acoustic converter for vibrating or generating a sound with an electric signal, and a method for producing the same.
Conventionally, in a portable terminal apparatus such as a mobile telephone, as means for notifying an incoming call, a small sound generator which generates a bell sound and a micromotor in which a weight is eccentrically attached to a rotation axis so as to cause vibration have been used as separate functional components. Furthermore, in order to listen to a conversation of a person on the other end of the line, it is required to attach a speaker for receiving a conversation.
FIG. 6 is a cross-sectional side view of an electric-mechanical-acoustic converter used in the above-mentioned portable terminal apparatus. The background art will be described with reference to this figure. In order to achieve further miniaturization and lighter weight of a portable terminal apparatus, the electric-mechanical-acoustic converter in FIG. 6 achieves both sound generation and vibration so as to reduce the number of components.
Referring to FIG. 6, an outer peripheral portion a circular diaphragm 1 is attached to a case 2. The case 2 has a bottom plate 5, and a yoke 3 is fixed to the bottom plate 5. A suspension 6 is supported by the case 2, and a magnet 4 is supported by the suspension 6. A voice coil 7 consisting of a bobbin and a coil both ends of which are connected to a terminal (not shown) to which an electric signal is input from outside is inserted in a magnetic gap formed by an inner peripheral surface of the yoke 3 and an outer peripheral surface of the magnet 4, and one end of the voice coil 7 is fixed to the diaphragm 1.
The yoke 3 and the magnet 4 form a magnetic circuit portion and the suspension 6 and the magnet 4 form a mechanical vibration system.
Next, the operation will be described. In the above-mentioned electric-mechanical-acoustic converter, an action-reaction force works between the voice coil 7 and the magnetic circuit portion, when an electric signal is applied to the voice coil 7 from outside. Suppose that a force applied to the voice coil 7 is an action force, the diaphragm 1 to which the voice coil 7 is attached vibrates due to the action force.
Furthermore, due to the reaction force applied to the magnetic circuit portion, the magnet 4 supported by the suspension 6 vibrates, and vibration is transmitted to the case 2 through the suspension 6, whereby the case 2 vibrates. The resonance frequency of the magnetic circuit portion is in a low band. Therefore, an electric signal at a frequency in this low band is applied to the voice coil, whereby outstanding vibration can be obtained.
However, there is a possibility that the portable terminal apparatus such as a mobile telephone is dropped while being carried due to its portability, and there is a possibility that an electric-mechanical-acoustic converter built in the portable terminal apparatus will be deformed and damaged by the shock caused by such a drop.
The present invention solves the above-mentioned problem, and its objective is to provide an electric-mechanical-acoustic converter which has outstanding resistance to shock and in which the resonance frequency of vibration is stabilized.
The entire disclosure of U.S. patent application Ser. No. 09/331,902 filed Aug. 16, 1999, is expressly incorporated by reference herein.
In order to solve the above-mentioned problem, the electric-mechanical-acoustic converter of the present invention includes a diaphragm, a magnetic circuit disposed so as to oppose the diaphragm, a voice coil one end of which is attached to the diaphragm and which is inserted into a magnetic gap of the magnetic circuit with a predetermined space, a weight integrated with the magnetic circuit or attached thereto as a separate component, at least one suspension supporting a movable portion composed of the magnetic circuit and the weight, and a frame supporting the diaphragm and the suspension, a space in an elastic deformation range of the suspension being provided between the outer periphery of the movable portion and the frame. Even in the case where the portable terminal apparatus is dropped, and the electric-mechanical-acoustic converter built therein is subjected to shock, the outer periphery of the movable portion is received by the frame, whereby the suspension can be prevented from being permanently deformed.